ABSTRACT E-cigarettes (e-cigs) have become increasingly popular, but their acute and chronic health effects are mostly unknown. Conventional cigarette smoking increases the risk of cardiac arrhythmia by slowing ventricular repolarization and inducing QT interval prolongation on the electrocardiogram (ECG). E-cigs produce several of the harmful and potentially harmful constituents (HPHCs) found in cigarette smoke. When aerosolized, the e-cig solvents propylene glycol (PG) and vegetable glycerin (VG), may similarly affect repolarization. Our preliminary data indicate exposure to e-cig solvent aerosols of equal-ratio PG and VG (PG:VG) prolongs QT and alters gene expression of ion channels key for repolarization in the mouse heart, suggesting inhalation of e-cig solvent aerosols may convert the heart into an arrhythmogenic substrate. However, e-cigs produce HPHCs at levels that vary markedly according to device characteristics, operating conditions, and use patterns. Thus, the full spectrum of their health impacts remains unclear. This project is designed to identify specific device characteristics and e-cig constituents associated with cardiac toxicity. It will apply both ECG and programmed stimulus electrophysiology (EP) studies to test the hypothesis that e-cigs induce electrical disturbances in the heart and that these effects depend upon e-cig characteristics and constituents. The studies will 1: Determine how device characteristics influence the acute electrophysiologic effects of e-cigs in mice, and 2: Assess the impacts of chronic e-cig exposure on cardiac electrophysiology and hemodynamics. Real-time cardiac physiology will be monitored through ECG telemetry during and after acute exposures to PG:VG aerosols from e-cigs of various characteristics (device type, user settings, nicotine levels), to delineate how they affect both HPHC production and ECG measures of cardiac dysfunction. The device characteristics with the greatest and slightest acute cardiac effects will then be selected for chronic exposure studies, in which cardiac EP and hemodynamics will be comprehensively assessed through telemetry, echocardiography, programmed electrical stimulation of the heart, molecular and histologic assays, aerosol assessments of HPHCs, and analyses of biomarkers of HPHC exposures. All exposure groups will be simultaneously compared to cigarette smoke and filtered-air exposure groups. Our research plan is responsive to the research priorities of the FDA/CTP, especially the interest area of toxicity. We expect that our results will elucidate the relative toxicity of different e-cig devices, constituents, and settings, and provide novel and significant insights into how each influences the arrhythmogenic potential of e-cig aerosols. We believe the outcome of our project would provide comprehensive and rigorous data to guide policies on e-cig product standards and to inform regulatory authorities of the cardiac risks associated with specific e-cig constituents and characteristics.